Aesculetin Exhibits Strong Fluorescent Photoacid Character.

Coumarins are bioactive molecules that often serve as defenses in plant and animal systems, and understanding their fundamental behavior is essential for understanding their bioactivity. Aesculetin (6,7-dihydroxycoumarin) has recently attracted attention due to its ability to act as an antioxidant, but little is known about its photophysical properties. The fluorescence lifetimes of its neutral and anion form in water are 19 ± 2 ps and 2.

Fluorescence of Scopoletin Including its Photoacidity and Large Stokes Shift.

Scopoletin is highly fluorescent in water and acts as a photoacid exhibiting excited-state proton transfer, ESPT, competitive with fluorescence. Its absorbance and emission spectral characteristics yield ground-state and excited-state pK values of 7.4 ± 0.